OpenSchema

OpenSchema provides a declarative implementation of (McKeown 1985) document
structuring schemata. Schemata are a widespread strategic generation
solution, targetting texts where the structure has got fixed after a
period of time (so no reasoning process can re-create this
structure).

What is strategic generation?

Strategic generation is the stage of a generation system
that decides what to say, compared to the tactical generation
component, that decides how to say it. It involves selecting the
relevant content to include in the output (Content Selection)
and imposing an order to it (Document Structuring).

The name strategic generation and the division into two
modules is one of the eldest architectures in NLG. Current generation
architectures divide the system into at least three modules, text
planning (the strategic generation component), sentence planning and
surface realization (the tactical generation component). The RAGS
project is a recent example of a concensus architecture.

What are schemata?

Document Structuring Schemata are a means to do strategic
generation. Starting from a pool of coarsely relevant knowledge (the
relevant knowledge pool), schemata are finite state machines
with terminals in a language of rhetorical predicates.

In her work, McKeown analyzed a number of texts in different genre
(all of expository in nature) and found out four different
organizational strategies that captured a large number of texts. She
termed these four strategies as ``schemata.'' and defined them as

(...) a representation of a standard pattern of discourse
structure which efficiently encodes a set of communicative
techniques that a speaker can use for a particular discourse
purpose. It defines a particular organizing principle for text and
is used to structure the information that will be included in the
answer. It is used to guide the generation process,
controlling decisions of what to say when in the text.

(McKeown, 1985, p.20)

OpenSchema extends McKeown's work by providing a declarative
definition of her predicates, now not necessarily rhetorical in nature
(a more appropriate name for these predicates is communicative
predicates).